Sighting device



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SIGHTING DEVICE Filed Jan. 12, 1943 5 Sheets-Sheet 1 FIG. I.

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Dec. 17, 1946. w. B. KLEMPERER ET AL 2,412,585

SIGHTING DEVICE Filed Jan. 12, 1943 5 Sheets-Sheet 2 INVENTORS film/P5256, maaaea,

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SIGHTING DEVICE Filed Jan. 12, 1943 5 Sheets-Sheet 3 INVENTORS [fi/PLQER,

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W. B. KLEMPERER ET AL SIGHTING DEVICE Filed Jan. 12, 1943 5 Sheets-Sheet 5 W01 raw/v5 5. KLEA/PEEEE, Syn/v5) r/T GOLDBERG,

Patented Dec. 17, 1946 SIGHTIN G DEVICE Wolfgang B. Klemperer, West Los Angeles, and

Sydney J. Goldberg, Los Angeles, Calif., assignors to Douglas Aircraft Company, Inc.,

Santa Monica, Calif.

Application January 12, 1943, Serial No. 472,168

Our invention relates to a sighting device and has particular reference to a device for determining and indicating the release point and the course to be followed by a projectile launched from a moving vehicle and intended to strike a moving target.

In the conduct of a war, it is often necessary to launch an explosive filled projectile from a moving vehicle such as an aeroplane or boat in such manner that the projectile will collide with a selected target which may be either moving or stationary. In order for the desired collision to result, it is of course necessary that the projectile be launched at a predetermined point and in the proper direction, and it is therefore necessary that the pilot of the vehicle be provided with some means for determining a suitable release point and the corresponding course direction of the projectile.

One of the most important and most comp e problems in this connection is to be found in the launching of the torpedoes from aircraft with the intent to torpedo a moving surface vessel such as a warship. The determination of a suitable release point and the corresponding torpedo course involves the proper correlation of many factors, both variable and fixed, among which may be enumerated (1) The altitude of the aircraft at the time the torpedo is launched;

(2) The velocity of the aircraft at the instant of launching;

(3) The torpedo travel range;

(4) The angular relation between the course of the target and the course of the aeroplane;

(5) The speed of the target; and

(6) The speed of the projectile.

In addition to the problem of properly correlating these and other factors, there exists a further problem in that some of these factors cannot be directly determined and others are subject to magnitude variations during the time between the launching of the torpedo and its arrival at the target location and this requires the taking into account of still further factors which can be determined.

To achieve the utmost in accuracy, a sighting device of this character must provide for a precise measurement of the critical factors involved wherever this is possible and must also provide for a precise mathematical correlation of all of the determined factors. Furthermore, in order that the sighting device may be used by a pilot of an aircraft or other vehicle, it is necessary that the majority of its functions be performed auto- 19 Claims. (Cl. 3346.5)

matically so that a minimum number of simple operations will remain for the pilot to perform.

Prior sighting devices of the character to which this invention relates were not entirely satisfactory in that they either required too much attention or work on the part of the pilot as by requiring him to perform trigonometrical or nom0- graphical calculations while using the sight or were inaccurate in that they did not take into account certain of the factors vital to an accurate determination of the projectile release point and course. The prior devices were also inaccurate in that they required vital factors to be estimated or guessed at because no provision was made for computing some of these factors.

It is therefore an object of our invention to provide an improved sighting device for determining and indicating the proper release point and course of a projectile to be launched from a moving vehicle with the intent that it collide with a selected stationary or moving target.

It is also an object of our invention to provide a sighting device of the character referred to in the preceding paragraph, which includes a sighting means for defining a sighting line movable through an angle equal to the angular measurement of the apparent distance it is necessary to lead a moving target in order to cause the projectile to collide with that target, together with a drive means for so moving the sighting means.

It is an additional object of our invention to provide a sighting device of the character set forth in the preceding paragraphs which includes a calculating means for computing the lead angle from known controlling factors, said calculating means being operatively connected to the drive means for the sighting means to effect an automatic moving of the sighting means through the computed lead angle.

It is a still further object of our invention to provide a sighting device of the character hereinbefore referred to, which include a, means for measuring the angle through which the sighting device is actually moved, together with a comparing device for c mparing the le mo ement with the computed lead angle and so controlling the driving means as to move the sighting means in such direction and to such an extent as to establish equality between said angles.

It is also an object of our invention to-provide a sighting device of the character set forth in the preceding paragraphs, in which the sighting means is releasably connected to the drive means to permit the sighting means to be moved independently of operation of the drive means.

It is a still further object of our invention to provide a sighting device of the character hereinbefore referred to, which includes a selective control device by means of which the sighting means may, if desired, be secured to a position aligning the sighting line with the course of the vehicle upon which the device is mounted, or connected to the drive means, or free for manual movement to the selected position.

It is an additional object of our invention to provide a sighting device of the character set forth hereinbefore, which includes means for indicating arrival of the vehicle at the proper projectile release point.

It is an additional object of our invention to provide a sighting device which can beused as a torpedo sight as well as a gun sight in conjunction with guns mounted fixed upon the same aircraft.

Other objects and advantages of our invention will be apparent from a study of the following specifications, read in connection with the accompanying drawings, wherein:

Fig. 1 is a perspective view of a portion of the interior of the pilots compartment of an aircraft and illustrating in perspective the general form and appearance of the preferred embodiment of our invention;

Fig. 2 is a geometrical diagram illustrating the various factors involved in the determination of the projectile release point and the proper course to be followed by the projectile;

Fig. 3 is a side elevational view of the sighting means portion of the device of our invention;

Fig. 4 is an end elevational view of the device illustrated in Fig. 3;

Fig. 5 is a fragmentary cross sectional view taken substantially along the line V--V of Fig. 3 and illustrating certain details of construction of the drive means employed for the sighting means;

Fig. 6 is an enlarged longitudinal sectional view taken substantially along the line VI-VI of Fig. 5 and illustrating additional details of construction;

Fig. 7 is a fragmentary cross sectional view taken substantially along the line VIIVII of Fig. 6 and illustrating the details of construction of the selective latching means employed for controlling the permissible movements of the sighting means;

Fig. 8 is a cross sectional view taken substantially along the line VIII-VIII of Fig. 6 and illustrating the details of construction of a ranging device forming a part of the sighting device of our invention;

Fig. 9 is an elevational view illustrating the general form and appearance of a control member comprising an assembly of control devices by means of which various determined and selected factors involved in the determination of the projectile release point and course may be introduced into the calculating mechanism forming a part of the device of our invention;

Fig. 10 is a fragmentary sectional view illustrating the interior details of construction of the control member illustrated in Fig. 9;

Fig. 11 is a diagrammatic view illustrating the relationships in the various parts and the mode of operation of the angle measuring instruments included in the sighting means;

Fig. L2 is a block diagram illustrating the principle of operation of an electrical calculating device of our invention which computes the lead angle and controls the operation of the drive means so as'to move the sighting device to a position corresponding to the computed lead angle, and which also controls the ranging device comprising a part of the sighting device of our invention;

Fig. 13 is a geometrical diagram similar to Fig. 2 but illustrating the additional factors relating to the sighting problem occasioned by the aircraft following a "homing path; and

Fig. 14 is a view similar to Fig. 13 but illustrating one way in which the homing path difficulty may be avoided by following a straight air interception course.

General description Referring to the drawings, we have illustrated diagrammatically in Fig. 1 the interior of a pilots compartment of an aeroplane as including an instrument panel I surmounted by a windshield 2 which may be fitted between the instrument panel I and a roof or ceiling supporting member 3.

We have shown in Fig. 1 the preferred embodiment of our invention as including a sighting means indicated generally by the reference character 4. This device is preferably mounted for slidable movement upon a guide rail 5 which is extended laterally across the pilots compartment and supported by a suitably strong and rigid transverse member 6. As will be more fully described hereinafter, the sighting device 4 is slidably mounted upon the guide member 5 so that when not in use it may be positioned at the extreme side of the pilots compartment where it will be out of the way and so that it may be slid to any selected operative position such as that illustrated in Fig. 1 whenever a need for its use arises. Such operative position may be straight ahead of the pilot or somewhat to his right or left, depending on whether the sight is used as a gun sight or as a torpedo sight to attack a surface vessel approaching from the right or left.

The sighting device 4 includes a pelorus portion serving to define a line of sight I. The device is arranged to be angularly moved about a vertical axis 8 so that the sighting line I may be swung from side to side as desired. The mechanism of our invention includes also a manual setting device or control member 9 to be described in more detail hereinafter, the control member 9 being normally supported from the instrument panel I as by means of a bracket So so as to be available for use by the pilot of the aeroplane at any time. The control member 9 is connected by means of a cable It) to an electrical calculating device or computer H which is preferably mounted in some convenient location in the aircraft which need not be a location accessible to the pilot of the plane.

Calculation of torpedo course The preferred form of our invention which is illustrated and described herein is intended for use as a sighting device for torpedo carrying alrcraft and is intended to permit a pilot of such an aircraft to control the launching of the torpedo carried thereby so as to, as far as is possible, start the launched torpedo along a course which will surely effect a collision between the torpedo and the target vessel.

We have illustrated in Fig. 2 by means of a geometrical diagram the various factors which are involved in determining the proper course to be followed by the torpedo in order to cause a collision with the target vessel of a torpedo launched from a selected release point. It will be noted that Fig. 2 is drawn in two parts, the upper part comprising a plan view while the lower part comprises an elevational view illustrating the path of the torpedo after it is droped from the aircraft. This figure is an approximate representation of the conditions and relationships existing just prior to the launching of a torpedo in that it shows as straight lines certain portions of the flight path of an aircraft which are in practice usually curved. However, as is explained in detail hereinafter, the simplification effected by treating these curved paths as straight lines introduces an error which is so small as to have a negli ible effect upon the result obtained.

In Fig. 2 it is assumed that an aircraft I2 is proceeding along a course indicated by the line l3 at the time a target vessel TS is sighted. The vessel TS is assumed to be travelling in the direction indicated by the arrow [4 along a course indicated by the line l5 and at a velocity U.

It is assumed that by the time the aircraft l2 has reached the point illustrated in Fig. 2, the pilot has determined that the target TS is an enemy ship and has determined that he will attempt to sink the target ship TS by launching a torpedo at the same. Accordingly a sight is taken as illustrated by the dotted line l6 and the target course line I5 is determined in a manner to be described hereinafter, this angle being indicated in Fig. 2 as the angle and hereinafter referred to as the target approach angle. Thereafter the sighting device is employed to compute the lead angle which will be hereinafter referred to as When this angle is determined, the sighting device is turned astern of the target through theangle and the course of the aircraft [2 is then altered as indicated by the curve I! in Fig. 2 to swing the course of the plane I2 ahead of the target through an angle sufficient to again bring the sighting line to bear upon the target TS.

The procedure just described is one of several different approach techniques in aircraft torpedo attacks. It is with reference to this technique that the function of a sight constructed according to the invention will now be explained but the sight lends itself equally well to the use with other approach techniques.

The new course of the aircraft I2 is indicated by the line I8 in Fig. 2. The aircraft is, at the time of torpedo launching, assumed to be travelling in the direction indicated by th arrow 19 along'the course l8 and at a velocity V. When the aircraft reaches the release point RP, the torpedo is launched, the release point RP being situated a distance R (hereinafter termed the torpedo travel range) from the'point 0 where the intended collision between the torpedo and the target vessel TS will take place. At the time the torpedo is launched the target ship TS occupies the position illustrated in Fig. 2 by the ship outline bearing the reference character TS. After being launched the torpedo proceeds in the direction of the course I8 as indicated by the arrow 20 in Fig. 2 with a velocity of varying magnitude which may be represented by an average velocity X which is associated with the torpedo travel range R.

At the instant of torpedo launching there exists a sighting or interception triangle comprising the intended torpedo course l8 extending from the release point RP to the collision point 0, this side of the triangle having a length equal to the torepdo travel range R; a sighting line 2| extended from the release point RP to the center of the target ship TS when in the position illustrated by the outline TS, the sighting line being disposed at the lead angle relative to the course of the plane l2 and the course of the torpedo and having a length equal to the sighting range Y. The third side of the triangle comprises the extension of the target ship course I5 extending from the ship position TS a distance D to the collision point 0 and making the angle 0 with the sighting line 2|. The third angle of the triangle is the striking angle or angle of intersection of the target course 15 with the torpedo course 18 and is represented as the angle a in Fig. 2,

Reference to the lower half of Fig. 2 will indicate the vertical variations in the course of the torpedo after launching. In this portion of Fig. 2 it is assumed that prior to the arrival of the aircraft I 2 at the release point RP the aircraft is flying along the course IS with a velocity V at a constant altitude H. When the aircraft arrives at the release point RP the torpedo is released and so falls by gravity to the surface of the water. In so falling the torpedo pursues a substantially parabolic course such as is indicated by the curved line 22. The principal dimensions of this parabolic course comprise the altitude H at the origin of the curve and the horizonta1 distance 111 through which the torpedo travels due to its initial forward velocity V during the time of fall from the altitude H to the surface of the water. Upon striking the water the torpedo submerges to a certain depth and then rises to the normal propulsion depth for which the torpedo was set, this part of the torpedo course being indivated by the double curved line 23 in Fig. 2. The speed of the torpedo during this part of its course will for convenience be represented by the term Va.

After the torpedo has traversed the distance d2 it will have decelerated to its normal propulsion velocity, to which velocity W is assigned. The remainder of the torpedo travel until the collision point 0 is reached covers a distance d3.

For convenience in calculation we have employed the symbols t1, t2, and is to indicate the respective times required for the torpedo to traverse the distance d1, (12 and d2.

If it were not for the fact that the torpedo traverses the first part (d1) of its path in air at essentially the same speed as the air speed (V) of the aircraft and the last part of its path ((13) in water at the much lower propulsion ve locity (W) of the torpedo, and if it were not for the fact that the time (in required for the first part (d1) of the path does not depend on the torpedo travel range (R) whereas the time (ts) required for the last part (d3) of the path does, the shape of the interception triangle (RP, 0, TS) would not be affected by the torpedo travel range (R) and it would not matter atwhich range the torpedo was launched provided the correct value of the lead angle was used. However, because of the difference in times and velocities just noted, the range, once chosen, does have a corrective influence upon the proper lead angle. It is therefore necessary to choose a suitable torpedo travel range and then evaluate the lead angle which is associated with the selected range. The choice of the torpedo travel range is ordinarily made by the pilot of the aircraft after appraisal of the tactical situation. It is therefore assumed for the purpose of this analysis that the pilot of the aircraft l2 arbitrarily selects the torpedo travel range R at which the torpedoing operation will be performed.

It is further assumed that at the time the pilot of the aircraft l2 decides to attempt to torpedo the target ship TS the velocity V of the aircraft and its altitude H are known. It is also assumed that the normal propulsion velocity W of the torpedo is known, that the deceleration time t2 of the torpedo has been previously determined, and that the pilot of the aircraft 12 having observed the target ship TS is able to recognize the nationality and type of ship and from the manner in which it is travelling through the water is able to determine from data previously compiled the probable value of the velocity U of the target ship TS.

Having determined these various factors, the pilot sets the angle 6 on the sighting device of our invention and effects an automatic calculation of the lead angle The basis for this calculation may be readily understood from the following analysis.

It is obvious that in order to effect the desired collision between the torpedo and the target ship TS the time which is required for the target ship to travel from the position TS to the collision point must necessarily equal the time required for the torpedo to travel from the release point RP to the collision point 0. Using the symbol T to represent this time, it may be said that T=D/U=R/X (1) From this it may be said that D/R=U/X (2) From the law of sines, it may be noted that D/R=sin /sin 0 (3) and, therefore,

sin qs/sin 0=U/X (4) and sin

Since U and 0 are both determined quantities, it is necessary only to evaluate X in order to permit the calculation of the angle 45. X, it will be recalled, is the average velocity of the torpedo in traversing the torpedo travel range R from the release point RP to the collision point ll. Thus X=R/T (6) This may be written r l+ 2+ 3 I A- 1+ 2+ 3 (7) since the sum of the distances d1, d2 and d3 equals the distance R, and the sum of the times t1, t2 and t3 equals the total time T.

The time n is the time required for the torpedo to fall from the altitude H to the surface of the water. Thus where g is the acceleration of gravity. The distance d1 may be expressed in terms of the forward component of velocity of the torpedo and the time ti as In the preceding equation, the forward component of velocity of the torpedo has been taken as equal to the velocity V of the aircraft. This is sufficiently accurate for all purposes when there is no wind. However, if there is a wind, the term V must be used to express the ground speed flight in a conventional manner, an appropriate i correction for head or tail wind component may be effected by an appropriate addition to or subtraction from the observed air speed of the aircraft.

The transverse component or cross wind can perhaps best be compensated for by so side-slipping the aircraft into the wind as to assure yawless entry of the torpedo into the water, although other corrective measures may be adopted as desired.

The velocity Va which has been assigned to the torpedo during the time t2 may, inasmuch as this time it is thereby defined, be taken as an average of the initial and terminal torpedo velocities. In other words Va= /2(V+W) (10) The distance (12 may be expressed in terms of the average velocity Va. and t2 (which is assumed to be known from experiment) thus:

Substituting this expression for X in Equation 5, supra, gives for the determination of the followingexpression sin 0 The foregoing derivation is given as an example of one sighting problem involving the enumerated variables. Other problems involving different factors or the taking into account of additional variable factors will, of course, change the equation derived. It will be realized, however, that in such event the principles and the fundamental relationships are the same as described.

From the foregoing it is apparent that the determination of the angle p depends upon determining and properly correlating the velocities U, V and W, the distances H and R, the time t2 and the setting of the angle 0- The manner in which these various factors are correlated and the manner in which the angle 0 is set on the sighting device will become apparent as the description of the device proceeds.

The sighting mechanism Figs. 3 through '7 illustrate the details of construction of the actual sighting mechanism portion of the sighting device of our invention. As

is best shown in Fig. 6, the sighting mechanism 4 includes a bracket 24 fitted with guide members 25 and 26 adapted to engage the guide rail 5 in such manner as to accurately maintain a predetermined alignment between the bracket 24 and the guide rail 5.

Preferably the bracket 24 supports a mechanism permitting the bracket to be immovably clamped to the guide rail 5 or released therefrom, as desired, to permit the bracket to be slid along the length of the guide rail. This mechanism may include a spring handle 21 secured to a transverse shaft 28 suitably journalled in the bracket 24. Upon the shaft 28 there is mounted a cam member 29 so positioned as to dispose a cam face 30 adjacent and parallel to one of a pair of inclined surfaces 3| formed on the guide rail 5, the other of said pair of surfaces 3| being engaged by an adjustable shoe 32. A torsion spring 33 looped behind the cam 29 and engaged with the bracket 24 normally urges the cam face 30 into pressure engagement with the adjacent inclined surface 3| and so clamps the guide rail against the guide members 2526 and the shoe 32 to thereby lock the bracket 24 against movement along the guide rail 5. Movement of the handle 21 in a counterclockwise direction as viewed in Fig. 6 overcomes the spring 33 and moves the cam face 30 away from the rail 5 and so releases the bracket 24 for free sliding movement along the rail 5.

The construction just described allows the sighting means 4 to be slid to one side; out of the way, and allows it to be moved into and locked in an operative position when its use is desired. This mechanism also permits lateral adjustment of the position of the sighting means 4 when in use so that the pilot of the aircraft may move the sighting means 4 to one side or the other of a position directly in front of his head to thereby relieve the pilot of the necessity of moving his head to one side or the other when sighting at an angle to his own flight path in an attack upon a target vessel moving either toward the right or left of his own original course.

The bracket 24 supports a fixed member 34 which is of inverted cup-shaped form, being characterized by an open bottom and a hollow interior defining an interior space 35. The open bottom of the member 34 supports a journal ring 36 which may be secured to the fixed member 34 as by means of threads 31. The journal member 36 coacts with a similar journal member 38 which is secured as by means of threads 39 to a housing portion 40 of the sighting device, thus journalling the housing portion 46 for pivotal movement about a vertical axis 4|. The journal members 36 and 38 may be locked to the housing member 40 as by means of lock rings 42.

The housing member 40 in turn supports the pelorus portion of the sighting device, which portion includes an angled housing 43 comprising a vertically disposed portion 44 and an angularly disposed portion 45.

The lower end of the vertical housing portion 44 is open and a lens 46 is secured therein as by means of the usual threaded mounting ring 41. The lens is positioned with its optical axis 48 vertical in a position to intersect the center of a reflector or mirror 49 positioned behind an opening 59 formed in the upper part of the housing 43 and covered as by a cover 5|.

From the outermost end of the angled housing portion 45 a bracket 52 extends which supports a lamp socket 53 carrying an incandescent electric lamp 54. The socket 53 and lamp 54 are enclosed by an openable cover 55 hingedly secured as at 56 to the end of the housing portion 45 and adapted to be held in its closed position as by means of a spring grip 51.

The outermost end of the inclined housing portion 45 is closed by an end wall 58 which is pierced with an aperture 59 in which is mounted a recticule 60. the latter being held within the opening 59 as by means of a mounting ring 6|. The recticule 60, lamp 54 and mirror 49 are so positioned that light projected from the lamp 54 10 through the center of the reticule 69 will strike the center of the mirror 49 and be reflected thereby along the optical axis 48 of the lens 46.

Below the lens 46 there is positioned a partially reflecting mirror 62, the same being mounted in a suitable mounting bracket 63 which is pivotally secured to the forward edge of the housing portion 44 as by means of a pivot shaft 64. The partially reflecting mirror 62 is normally disposed at an angle of approximately 45 relative to the optical axis 48 of the lens 46 so that as the pilot or the user of the sighting device looks along the sighting line I he will see through the mirror 62 any objects which may be located on the extension of the sighting line 1 and will see also the reflection from the surface of the partially reflecting mirror 62 the image of the reticule 60 as reflected by the mirror 49 and transmitted by the lens 46.

The lens 46 is positioned a distance equal to its focal length from the reticule 60 so that the image of the reticule seen by the pilot in looking along the sighting line I will appear to be located a great distance away. This serves to superimpose upon the object actually seen through the partially reflecting mirror 62 the greatly magnified image of the reticule 69. The reticule 69 preferably includes cross-hairs or like representations which define the axis of the sighting line and the parts are so collimated that the apparent superimposition of the reticule crosshairs upon the object actually situated on the sighting line will occur precisely at the intersection of the sighting line with the object, independently of whether the observers eye is slightly displaced from the optical axis 1 within the aperture of reflected image of the lens 46.

It will be appreciated, of course, that if the device described is mounted on an aeroplane flying at a considerable altitude and it is desired to take a sight on a surface vessel under circumstances making-it undesirable to depress the nose of the aircraft, it will be necessary to depress the line of sight below the horizontal to an inclined line la which is illustrated as a dotted line in Fig. 6. On the other hand, it is intended that the sighting means 4 be used alternatively as a torpedo director or as a sighting device for aiming fixed guns mounted on the aircraft to fire forward in a direction substantially parallel to the axis of the plane. It is, therefore, desirable to provide an adjustment means whereby the direction of the substantially horizontal sighting line 1 may be adjusted vertically to bore-sight the fixed guns and it is also desirable to provide an indexing means to permit the bore-sighted line 1 to be re-established as desired after being depressed to the inclined line la as described.

For these reasons, the pivot shaft 64 also pivotally supports an upwardly directed adjustable stop member 65 which is apertured to receive a screw 66 secured to a suitable boss 61 provided on the housing portion 44. Adjusting nuts 68 are threaded upon the screw 66 on opposite sides of the stop member 65 to permit adjustment of the angular position of the stop member 65. The stop member 65 also extends downwardly alongside the mirror bracket 63 and provides near its lower end a stop surface 69 which is engaged by the peripheral surface of an eccentric member 10 pivotally mounted upon the bracket 63. A torsion spring 1| (Fig. 3) surrounding the shaft 64 and inter-engaging the bracket 63 with the stop member 65 serves to continuously urge the mirror bracket 63 upwardly to at all times main- 11. tain the eccentric 10 in engagement with the stop surface 69. A spring and notch arrangement I2 or other suitable detent construction is employed to index and yieldably hold the eccentric member 10 in a normal or bore-sighted position such as is illustrated in Fig. 6. A handle 13 permits the eccentric I to be manually rotated in a clockwise direction and the eccentric member is so positioned that such rotation will decrease the distance between the pivot and the peripheral surface of the eccentric member I0, thus allowing the spring II to move the mirror bracket 63 upwardly and effect a depression of the sighting line 1 to a position such as that occupied,

. for example, by the line la.

The adjusting nuts 68 are employed to adjust the vertical position or direction of the sighting line I when the eccentric member is in its normal or bore-sighted position to thereby sight in the fixed guns of the aircraft, and the detent arrangement l2 insures the re-establishment of this adjustment after the eccentric is rotated to depress the line of sight.

If desired, the pivot shaft 64 may also pivotally support a bracket 14 upon which is mounted a polarizing filter I5, permitting the filter to be swung to a position such as that illustrated by the solid lines in Fig. 3 to provide for better sighting in those instances where the glare from the surface of the water is a considerable hindrance.

Since, as above stated, it is intended that the device be used as a fixed gun sight as well as a torpedo director, it is therefore necessary also that provision be made for indexing the sighting device in such manner as to substantially align the sighting line I in a horizontal plane with the axis of the aircraft, it being recalled that the housing 40 and the pelorus portion enclosed by the housing portion 43 are mounted for pivotal movement relative to the aircraft about the vertical axis 4| by means of the coacting journal members 36 and 38.

Accordingly, the housing portion 4o is extended upwardly into the space 35 within the interior of the fixed member 34. Upon the upper end of the housing member 40 we secure, as by means of screws, a mounting plate 16. The mounting plate I6 is journaled and threaded to receive a journal member 16a. within which an upper notch plate 17 is journalled as by the extension of a boss portion 18 thereof into a guiding aperture I9 formed in the journal member 16a. The notch plate H is best illustrated in Fig. 7 as comprising a semi-circular, disk-like portion 80 and a forwardly extending tailpiece SL The tailpiece 8| is disposed between a pair of adjusting screws 82 and 83 threaded in boss portions 84 and 85, respectively, formed on the mounting plate I6. Access to the screws 82 and 83 may be had through suitably positioned apertures 86 and 81 provided in the fixed member 34. A notch 88 formed in the peripheral edge of the plate 1! is positioned to receive a locking projection 89 formed upon an upper spring finger 90 secured as by means of screws 9| to the fixed housing portion 34 when the pelorus portion of the sighting device is turned to a position substantially aligning the sighting line I with the axis of the aircraft. In this position the projection 89 and notch 88 serve to hold the pelorus portion against rotation. The adjusting screws 82 and 83 permit shifting this indexed position for the purpose of bore sighting the fixed guns of the aircraft with respect to the horizontal plane.

To permit unlocking of the sighting device to permit the pelorus portion thereof to be turned to a position not substantially aligned with the axis of the aircraft, we provide a control knob 92 which is secured to a control shaft 93. The shaft 93 extends into the interior 35 of the fixed member 34 and is journalled in the member 34 as by means of a sleeve bearing 94.

Upon the inner end of the shaft 93 we affix a cam 95 which provides a rear cam face 96. This face engages the inner vertical surface of the spring member and is so arranged that when the the knob 92 is turned from the position illustrated in Fig. 6 through 90, the spring member 90 will be urged rearwardly or to the right as viewed in Fig. 7 a distance sufficient to withdraw the projection 89 from the notch 88 and thus release the pelorus portion of the sighting device.

Provision has been made for setting the approach angle 0; that is, the angle between the sighting line and the course of the target ship. This provision includes a target course arm 91 which is positioned immediately below a bottom closure 98 for the housing portion 40. The arm 91 is secured to a shaft 99 which is preferably coaxial with the vertical axis 4I about which the pelorus portion of the sight is pivotally mounted.

Within the interior space defined by the housing 40, we mount four rotary transformers identified, respectively, by the reference characters IOI, I02, I03 and I04. As will be more fully explained hereinafter, each of the transformers IOII04 comprises a primary winding and a secondary winding, the secondary winding being arranged as a stator and the primary winding being arranged as a rotor, the latter being mounted for angular movement within the stator windings.

The transformers are so constructed that when a fixed voltage is applied to the primary windings, the voltage induced in the secondary windings will vary in direct proportion to the sine of the angle through which the rotor is turned. The rotors of the transformers I02, I03 and I04 are mechanically interconnected with each other and are in turn connected to the shaft 99 so that the position of the rotors of these three transformers relative to the pelorus portion of the sighting means is defined by the angular position of the target course arm 91.

In operation the sight is first trained on the target ship, or alternatively the sight may be locked in a position aligning the sighting line 1 with the axis of the aircraft and the aircraft so guided as to extend the sighting line 1 to the target ship. The target course arm 91 is then turned to a position which in the best judgment of the pilot of the aircraft aligns the target course arm 91 with the observed course being pursued by the target ship. Experience has proven that the pilot of an aircraft can, by visual judgment, readily position the target course arm 91 in parallelism with the course of the target ship with sufficient accuracy to keep the calculated value of the lead angle 0 within the permissible limits of error.

The stators of the transformers I03 and I04 are mechanically connected to each other and to a sleeve I05 which is in turn fitted into an aperture provided in the lower closure 98. This serves to hold the stators of the transformers I03 and I04 in alignment with the pelorus portion of the sighting means while screws I05a extending through the bottom wall of the lower closure 98 and into the stator of the transformer I04 hold the stators I03 and I04 against rotation relative to the pelorus. Thus the above described a oma operation of turning the target course arm 91 to parallelism with the course of the target ship serves to rotate the rotors of the transformers I03 and I04 through an angle equal to the target approach angle. The manner in which the resulting voltage output of the transformers I03 and I04 is employed will be explained in detail hereinafter.

The stators of the transformers IOI and I02 are mechanically connected to each other and are also secured to a worm wheel I06. The worm wheel I06 and the stators of the transformers IOI and I02 are journalled for rotation relative to the stators of the transformers I 03 and I04 and relative to the pelorus portion of the sighting means by means of a. ring-like journal I01. This permits the stators of the transformers IOI and I02 to be rotated independently of the transformers I03 and I04.

It is intended that the amount of angular movement normally imparted to the stators of the transformers I! and I02 relative to the pelorus portion be equal to the lead angle and that these transformers be so arranged as to permit the pelorus portion of the sighting means to be turned to and indexed in a position such that the angle between the sighting line I and the axis of the aircraft be equal to the amount of angular movement of the stators of the transformers IOI and I 02 to the pelorus portion of the sighting device.

For this purpose we secure to the upper end of the stator of the transformer IM a notch plate I08. This plate is provided on its upper surface with an annular groove defining a tapered journal surface I09 which coacts with a similar surface formed on the under side of the journal member 16a and serves as a journal coacting with the journal I01 to support the transformer stators IOI and I02 for rotation within the housing 40. The notch plate I08 is provided with a notch IIO adapted to receive a projection III formed on a spring finger II2 secured to the fixed portion 34 of the sighting device and positioned immediately below the shaft 93 in a position to be engaged by the cam surface 96 of the cam member 95.

As clearly appears in Fig. 6, the cam surface 96 is so arranged that when the knob 92 is in the position shown in Fig. 6, the upper notch plate 11 will be locked to the fixed housing portion 34;

when the knob 92 is rotated through 90 from the I position illustrated in Fig. 6, the spring finger 90 will be withdrawn and the spring finger II2 will be held withdrawn so that neither the notch plate 11 nor the notch plate I08 will be held fixed relative to the fixed portion 34 of the sight; and when the knob 92 is rotated 180 from the position illustrated in Fig. 6, the upper spring finger 90 will be held withdrawn and the lower spring finger II2 will be released to allow the projection III to enter the notch H0 and lock the pelorus portion of the sighting device in such a position that the sighting line 1 makes an angle with the axis of the aircraft equal to the angle through which the stators of the transformers IOI and I02 have been moved relative to the pelorus portion.

The rotor of the transformer IOI is intended to be held fixed relative to the pelorus portion of the sighting device and-is accordingly secured to a vertically rising shaft I I3 which extends upwardly through an aperture provided in the upper notch plate 11 and is received in a split tapered threaded plug member H4. The plug member I I4 is threaded into a threaded tapered bore provided in a thickened portion of the upper notch plate 11 so that tightening the plug H4 in its threads will contract the same about the shaft II 3 and secure the same to the notch plate 11. Initial adjustment of the position of the shaft I I3 may be facilitated by the provision therein of a screw-driver slot H6.

The notch plate 11 also provides an upper coni cal surface II1 forming a Part of an upper bearing construction, the other part of which comprises a conical bearing surface II8 formed on an upper bearing member II9 pressed or otherwise secured in an aperture I20 formed in the fixed member 34. Access to the screw-driver slot II6 may be had through a bore I2I in the bearing member I I9 by removing a removable closure In order to permit the pelorus portion of the sighting device to be turned manually to a desired angular position, we mount within the housing 40 a worm gear I25 (see Fig. 5) which is supported upon a shaft I 26 suitably journalled within the housing 40 and so positioned as to engage the worm gear I25 with the worm wheel I06. The rearward end of the shaft I26 carries a gear I21 (see Fig. 4) which meshes with a gear I28 mounted upon a stub shaft I29. The stub shaft I29 carries an adjusting wheel or crank I30 by means of which the shaft I29 may be rotated.

It will be seen that rotation of the crank I30 will effect a relative rotation between the housing 40 and the worm wheel I06. If the worm wheel I06 and the stators of the transformers IM and I02 to which it is connected are held against rotation by engagement of the projection III with the notch IIO of the notch plate I08, this relative rotation appears as a rotation of the housing portion 40 about the vertical axis 4 I.

It is intended that this angular movement of the pelorus portion of the sight be effected automatically and for this purpose we have mounted within a housing I3I secured to the housing portions 40 and 44 a small electric motor, the armature shaft I32 of which carries on its upper end a worm gear I33. The worm gear I33 meshes with a worm wheel I34 secured to a stub shaft I 35. The stub shaft I35 is journalled for rotation in a support member I36 and carries on its rearward end a friction disk member I31. The friction disk member I 31 coacts with a friction plate I38 which is slidably mounted upon the shaft I26 and urged toward the disk I 31 as by means of a spring I39. Friction material I40 interposed between the members I 31 and I38 insures transmission of sufficient torque between the stub shaft I35 and the shaft I26 to effect rotation of the sight as above described.

The provision of the friction drive between the motor and the shaft I26 permits the sight to be turned through energization of the motor and also permits the sight to be turned manually through rotation of the crank I30, in which 1atter event rotation of the shaft I26 is permitted by slippage at the friction drive element I31-I38.

The structure above described permits either of two modes of operation of the sighting device. For example, the pelorus portion of the sighting device can be locked to the stators of the transformers IOI and I 02 by turning the knob 92 to the appropriate position. The crank I30 or, alternatively, the motor I32 may be operated to effect angular movement of the sighting device. According to another mode of operation, the knob 92 may be turned to a position in which the pelorus portion of the sight is disconnected from the stators of the transformers IM and I02. The crank I30 or the motor I32 may be operated to rotate the stators of the transformers MI and I02 through the desired angle. Thereafter the knob 92 may be turned to a position releasing the spring finger H2, whereupon the projection III will engage the periphery of the notch plate I08. The sight may then be grasped by hand and manually turned about the axis 4| until the proper angular position is reached, at which time the spring finger I I2 will move the projection I II into the notch I I and lock the pelorus portion of the sight in the desired angular position.

Preferably, the lower part of the housing 40 is provided with a protractor scale I23 adapted to coact with a suitable index carried by the target course arm 91 to permit direct reading of the approach angle 0. Similarly, the fixed portion 34 may carry a protractor scale I24 adapted to coast with a suitable pointer carried bythe movable housing portion 40 to permit direct reading of the angle through which the pelorus portion is turned. These protractor scales permit settings to be made in accordance with mental trigonometric calculations for special problems for which the electrical calculating device may not be adjusted or in the event the electrical apparatus fails.

The manual setting device In addition to the sighting device just described, the mechanism of our invention includes the manual setting device or control member 9 by means of which the magnitude of certain of the terms of the lead angle equation may be adjusted. This member is illustrated in detail in Figs. 9 and 10. As is shown therein, control member 9 includes an outer housing or case I4I comprising a hollow cylinder within which there are mounted five control units I42, I43, I44, I45 and I46. The interior space defined within the housing MI is divided into separate cells, one for each of the control units I42-I46, by transversely extending web members I47. The housing I 4| is cut away as indicated at I5I in Fig. 9 at the location of each of the cell-like spaces defined by the web members I41, the apertures I5I serving to provide access to dial members I52 mounted within each of the cell-like spaces in the housing MI. is bored centrally as indicated at I54 to receive the mounting sleeve portion I55 of an electrical potentiometer of conventional construction and referred to generally by the reference character The potentiometers I56 may each be immovably secured to an associated web I41 as by means of a clamping nut I51 threaded on to the sleeve I55. Each of the potentiometers I56 includes a resistance element I58 which is secured within a stationary housing portion I59. The resistance element I58 is engaged by a contact finger I60 which is mounted upon an insulating plate IBI secured to a shaft I62 journalled in the sleeve I55.

The dial members I52 above referred to may be secured to their respective insulating plates IBI as by means of rivets I63 so that rotation of the dial member I52 effects a relative movement between the movable contact I60 and the stationary resistance strip I58.

To facilitate such rotary movement of the dial member I52, the same is preferably provided with a raised and knurled portion I64. The cylindrical portion of the dial member I52 is adapted to be calibrated as is indicated in Fig. 9 and these Each of the web members I41 calibrations are adapted to coact with suitable index marks formed on the stationary cylindrical portions of each of the units to permit the potentiometers to be set in accordance with the determined magnitude of certain of the terms of the lead angle equation, one of such index marks being indicated by the reference character I65 in Fig. 9.

As clearly appears in Fig. 9, one end of the housing I4! is provided with means for attachment to the control member 9 of the multi-conductor electric cable I0, the various wires of which are connected in a manner to be described hereinafter to the various terminals of the potentiometers housed in the control member 9.

The control member 9 has been described as providing for the setting of five separate variable quantities, i. e., those required for the solution of the particular sighting problem which has been herein described as one specific example. It will be understood that a greater number or fewer potentiometers may be housed within the control member 9, depending upon the particular type of problem to be solved and the number of variables to be taken into account.

The electrical calculation of 5 The third portion of the mechanism of our invention comprises an electrical calculator by means of which the lead angle s is automatically computed. Fig. 12 of the drawings comprises a block diagram illustrating the principles and mode of operation of a calculator which may be used to determine the angle 1 and control movement of the pelorus portion of the sighting device through that angle.

In Fig. 12 each of the rectangles is intended to represent an electronic or vacuum tube unit such an as oscillator, a mixer stage, an amplifier stage or the like. The variable resistance symbol has been employed to represent the potentiometers of the control member 9 and the variable inductance symbol has been employed to represent the variable ratio transformers IOII04. The lines with the arrowheads affixed thereto and extending between the various parts of the apparatus indicate the course of an electrical signal through those various parts. The various legends inscribed near each part of the apparatus indicate the mathematical function performed by that portion of the apparatus and the matter inscribed in the rectangles is intended to represent the character of the electronic equipment designated by the associated rectangle.

As clearly appears from Fig. 12, the calculating device includes first a source I61 of alternating potential of constant voltage and frequency. We prefer to employ for this a vacuum tube oscillator normally operating to generate an alternating potential having a frequency of the order of magnitude of one thousand cycles, although other well known types of alternating potential generators may be used as desired. The voltage generated by the source N51 is applied as indicated at I68 to the input of the rotary transformer I04. Since the transformation ratio of this transformer is directly proportional to the sine of the angular displacement of the movable winding, the voltage output of the transformer I04 is likewise proportional to the sine of the angle through which the rotor of the transformer is turned.

Thus, if we assume a maximum transformation ratio of one to one and assume that the source I61 generates a voltage E, then the output of the transformer I04 will be e1=E sin (14) This output is fed as indicated at I69 to a potentiometer I comprising the unit I44 of the control member 9. The associated dial IE4 is so calibrated that with the voltage e1 applied across the entire resistance strip, the voltage between the movable contact and one end of the resistance strip will be where U is the velocity of the target ship, W is the normal propulsion velocity of the torpedo and K1 is the calibration constant of the potentiometer I10. Thus the voltage between the movable contact and one end of the resistance strip of the potentiometer I10 is e2=E(U/WK1) Sin 0 (16) This voltage is fed as indicated at IN to an amplifier stage I12, which is preferably of the electronic or vacuum tube type and which may be of conventional design and construction, as may all of the amplifiers and electronic circuits referred to hereinafter. The amplifier I12 may be adjusted to provide an overall gain equal to K1 and it will, for the purpose of this description, be assumed that it is so adjusted. However, as will more fully appear hereinafter, the gain equal to K1 may be obtained in any one or all of a number of the amplifier stages employed, but an understanding of the operation of the device is facilitated by considering the entire gain of K1 to be obtained in the one amplifier stage I12. The same considerations also apply to the gain of various other amplifier stages to be referred to hereinafter. Thus the output of the amplifier I12 is es=E(U/W) sin 0 (17) The voltage 63 is fed to a potentiometer I13 comprising the unit I43 illustrated in Fig. 9. The dial of this potentiometer is calibrated in terms of V, the velocity of the aircraft and the calibration is so arranged that the voltage output of the potentiometer I13 is This voltage is applied to an amplifier stage I14 whose overall gain is eoual to K2. Thus the output of the amplifier I14 is The voltage 65 is fed to a potentiometer I15 comprising the unit I42 illustrated in Fig. 9. The dial of this potentiometer is calibrated in terms of H, the altitude of the aircraft, and the calibration is so arranged that the voltage output of the potentiometer I15 is The voltage e-: is fed to a potentiometer I11 comprising the unit I48 illustrated in Fig. 9.

18 The dial of this potentiometer is calibrated in terms of R, the intended torpedoing range. This calibration is so arranged that the voltage output of the potentiometer I11 is The voltage 68 is fed to an amplifier stage I18, the overall gain of which is adjusted to be equal to K. Thus the voltage output of the amplifier I18 is e E(U/W) (V- W) sin 0 (23) The voltage e9 is fed to a mixer stage I19 as is also the voltage 63 as is indicated at I80. The outputs of the amplifiers I12 and I18 are so adjusted with respect to the time phase of their respective output voltages that the mixer I19 effects a subtraction of the voltage 69 from the voltage es. Thus the voltage output of the mixer I19 is 10 E(U/W) sin 0 1 1 E(U/W)(V W) 15 sin 9 24 This expression may be rewritten as t a E(U/IV)|:1 M l +:Ll] 9 2 Comparing this with Equation 13, supra, it will be noted that It should at this point be noted that among other things the potentiometer I10 operated to introduce the factor (l/K1) into the expression for ex. This was assumed to be cancelled-out by introducing the factor (K1) into the expression by making the gain of the amplifier stage I12 equal to K1. It will be apparent that if desired, the same result may be obtained by making the product of the gains of the amplifier I12 and that input channel of the mixer stage I19 which is associated with the potential e3 equal to Kl. Thus if desired the entire gain of K1 may be had at the mixer stage I19 if desired.

Similarly, there has been introduced into the expression for eg the factors (1/Kl),(1/K2),(1/K3) and (l/Ki). The efiect of these factors may be cancelled by making the product of the gains of the amplifier stages I12, I14, I16, I18 and that input channel of the mixer stage I19 which is associated with the potential es equal to thus permitting wide choice as to the gains of the individual stages.

The output of the source IE1 is also conducted as indicated at I8I to this input of the rotary transformer I M. It will be recalled that the stator of this transformer is adapted to be latched to the fixed housing portion 34 of the sighting device and that the relative angular positions of the rotor and stator of the transformer IOI corresponds precisely to the angular position of the pelorus portion of the sighting device when the notch plate I08 is locked to the fixed housing portion 34 by proper manipulation of the knob 92. Thus the angle through which the rotor and stator of the transformer IOI are rotated relative to each other represents the angle through which the sighting line 1 has been revolved with respect to the axis of the aircraft. This, the actual angular movement of the sighting device will be referred to as the angle ,6. Thus if the 19 voltage input to the transformer IOI is equal to E, the output voltage is el1==E sin (2'?) The voltages em and cm are each fed to a mixer I82 and the phase relation of the voltages em and an is so adjusted that the mixer effects a subtraction of these two. By this the voltage output of the mixer I82 is made The voltage output an is amplified by a power amplifier I83 and applied to a phase selector I84 and polarized relay I85. Referring to Equation 28, supra, it will be observed that if the angle 5 is smaller than the angle the potential e12 will be expressed with a plus sign, whereas if the angle 5 is increased sufficiently to exceed the angle (p, the sign of 612 will change from plus to minus. Because era is the magnitude of an alternating potential, the plus and minus signs just referred to are meaningless as regards polarity of the potential except at a given instant. Thus, in reality, a change in sign from plus to minus (or vice verse) of the voltage e12 signifies a complete 180 reversal in the time phase of the voltage.

The phase selector I 84 is arranged to be responsive to reversals of phase of the voltage em as by comparing the time phase of the voltage em with the time phase of a constant voltage en derived from the source I61 and amplified as by an amplifier I8'5a.

The phase selector I84 is arranged to control the polarized relay I 85 to operate the same in one direction when on partakes of a plus sign and in an opposite direction when the sign of 612 goes minus. The relay I85 is in turn connected to control the motor I32 in such manner as to rotate the motor I32 in one direction when sin s exceeds sin [3 and in the other direction when sin e exceeds sin s. The directions of rotation of the motor I32 are so chosen that when energized the motor tends to rotate the stator of the transformer IllI in such direction as to bring E sin 5 toward equality with E sin o. Thus the motor I32 will operate automatically to turn the notch plate I88 to a position such that the angle [3 through which it has been rotated is equal to the angle as determined by the electrical calculator. When ,3 and are equal, 212 becomes zero and the polarized relay I85 assumes a neutral position de-energizing motor I32.

The motor I32 may be of any suitable type capable of having its direction of rotation reversed by a double-throw relay. A split-series field commutator motor has been found suitable.

It will thus be seen that the calculating device just described coacts with the motor I32 so as to effect an automatic angular shifting of the pelorus portion of the sighting device by an amount equal to the lead angle The direction of measurement of the angles is so taken that the angular displacement of the sighting line I is opposite to the direction in which the target ship TS must be led so that the pilot of the aircraft, by angularly changing the course of the aircraft in the direction in which it is necessary to lead the target ship TS, may bring the sighting line I to again bear upon the target ship. By then holding the sighting line I on the target ship, the pilot of the aircraft is permitted to maintain a course along which the torpedo must travel in order to intercept the target ship at the collision point 8.

e12=E (sin sin p) It will be noted that the pilot of the aircraft may efiect this automatic setting of the sighting device by performing the following operations. Upon observing the target ship TS, the sight is brought to bear on the target ship TS. This may be accomplished by any one of three different operations; (a) the pelorus portion of the sight may, by manipulation of the knob 92, be latched to the lower notch plate I08 and the hand crank I38 operated to turn the sight, (b) the knob 92 may be moved to its neutral position and the pelorus portion of the sight may be grasped and turned by hand, or (c) the sight may be aligned with the axis of the aircraft as by turning the knob 92 to the position illustrated in Fig. 6 to latch the sight to the fixed portion 34 and the aircraft so guided as to bring the sight to bear on the target ship.

While the sight is held on the target ship TS, the target course arm 91 is turned to parallelism with the estimated course of the target ship TS. The sight is then released as by turning the knob 92 to a position displaced from that illustrated in Fig. 6. Thereafter the pilot, having recognized the nationality and type of the target ship TS, may from his own knowledge set the potentiometer H0 to a point corresponding to the estimated speed of the target ship. The pilot then appraises the tactical situation and chooses the torpedo travel range at which he will torpedo the ship and from what altitude the torpedo will be dropped. The respective distances are then set by means of the potentiometers I15 and Ill. The pilot also decides upon the speed at which he will fly the aircraft at the time the torpedo is released and this speed is set on the potentiometer I13.

If the electrical calculator is in operation during the time these settings are being made, the motor I32 will be energized as required by the changes efiected by changing the potentiometer settings. As soon as the last setting is made, the motor will rotate the notch plate I08 to a position in which the notch plate is displaced from its original position by an amount equal to the lead angle o. The pilot may then turn the knob 92 to a position displaced from that illustrated in Fig. 6 and then by grasping the pelorus portion of the sight turn the sight in the required direction until the projection III snaps into the notch H8. The sighting line I is thus displaced from the axis of the aircraft by the lead angle 1: and the pilot then changes his course to bring the sighting line I to bear upon the target ship. When this is accomplished, the subsequent release of the torpedo will result in the torpedo being started along the proper course to intersect the target ship at the collision point 0.

If desired. the pilot of the aircraft, instead of turning the sighting device by hand until the projection III engages the notch IIO, may after setting the target course arm 9! turn the knob 92 to a position displaced 180 from that illustrated in Fig. 6 to thereby immediately engage the projection III with the notch I I8. Thereafter the operation of the motor I32 resultin from setting up on the control member 9 the various factors involved in the calibration of the angle will result in the sight being turned automatically to the corresponding angular position.

Additional aspects of the torpedo course problem As was pointed out hereinbefore (column 5 supra) the preceding analysis relating to the calculation of the torpedo course was based upon 21 the assumption that the flight path of the aircraft along the line l3 before the veering -l1 and along the line [8 after the veering defined straight lines. Under ordinary circumstances the real paths I3 and I8 followed by the aircraft are curved due to the simultaneous progress of the target ship TS and the aircraft 12 while the aircraft is being so piloted as to maintain the sighting line dead on the target ship. These curved paths are of the type commonly referred to as homing paths and are illustrated in Fig. 13 which is a diagrammatic view similar in all respects to Fig. 2 hereinbefore discussed except for the fact that it illustrates the curved shape of the homing paths.

As a general proposition, however, the aircraft velocity V is of the order of four or five times the velocity U of the target vessel, with the result that the curvature of the homing paths is very slight so that the slight curvature actually present has no significant influence on the geometry entering into the calculation of the lead angle 4). Such path curvature as does occur, however, has the effect of slightly increasing the observed approach angle before the veering maneuver l1 and of slightly decreasing the observed approach angle 0 after the veering l1 and during the time the aircraft is following the course l8.

Although in most instances the variation of the approach angle'o will be imperceptible, our invention permits the pilot to take any perceptible change of this angle into account and permits an instantaneous adjustment to correct for the' perceived change in the approach angle by readjusting the target course arm 91 anew into visual alignment with the course of the target. Such a readjustment of the position of the target course 9! will instantly correspondingly change the calculated value of the angle and will cause the electrical calculator portion of our invention to operate the motor I32 and readjust the angular position of the pelorus portion of the sight to establish the corrected sighting line.

As an alternative procedure the curvature of the initial approach path l3 can be entirely avoided by making this part of the approaching on a straight air interception course I 3" illustrated in Fig. 14. The air interception course I3" is so chosen that if the aircraft were to continue therealong it would pass directly over the target vessel at the point indicated in Fig. 14 as TS".

In this procedure the target does not appear dead ahead of the aircraft during the initial approach but at a constant air interception lead angle which may be denoted by the symbol This angle is defined by the law of sines in the air interception triangle as sin "=U/V sin 0 (29) Our invention is adapted to the ready execution of this alternative procedure. All that it is necessary for the pilot to do is during the preliminary approach phase [3 to swing the pelorus portion of the sight (as by engaging the latch with the notch H0 of the lower notch plate I08 and turning the crank [30) through the angle to a position so selected that upon continued approach no course change of the aircraft is required to keep the sighting line on the target vessel. Experience has shown that no great accuracy of this adjustment is required and that in fact a very rough estimate of the air interception lead angle willgenerally sufiice to make the approach path straight for all practical purposes.

The sighting device as a gun sight Reference has-been made hereinbefore to the alternative use of the device of our invention as a gun sight for sighting guns which are mounted on the aircraft in a fixed position adjusted to fire straight ahead of the aircraft. It has been pointed out that the sight may be adjusted for this use by latching the pelorus portion of the sight to the fixed portion 34 of the sight by turning the control knob 92 to the position illustrated in Fig. 6 to engage the latch with the upper notch plate 11 and by turning the Vertical adjustment handle 13 to a position engaging the eccentric member 10 With the detent arrangement 12, the adjusting nuts 68 and the horizontal adjustment screws 82 and 83, providing, respectively, for vertical and horizontal bore-sighting adjustments to be made.

At this point it is desired to point out that the collimating type of sighting means illustrated herein possesses advantages that cannot be realized through use of the ordinary gun sighting devices such as the conventional ring and bead sight. The principal advantages are that it is not necessary for the user of the sight to maintain the eye which he is usin to sight the target in precise alignment with two fixed sighting points as is the case with the ordinary ring and bead sight but instead is permitted considerable latitude as to the lateral, vertical and fore and aft positions of the eye being used to sight the target. Further, the collimating type of sight causes the reticule cross-hairs to appear to be projected on to the target itself so that the intersection of the cross-hairs defining the line of sight appears in focus to the pilot the same as does the target itself, whereas with the ordinary ring and bead sight it is impossible to simultaneously maintain the sighting elements and the target in focus. Consequently with the ring and bead sight the actual sighting elements used are seen in a hazy and blurred manner when a sight is taken on the target, with the result that it is dimcult to determine whether or not the sight is taken as accurately as is desired. This difficulty is completely avoided through the use of the collimating type of sight.

In the alternative use of the device of our invention as a gun sight for guns fixed on the aircraft, it may be desirable to introduce a lead angle when firing at a moving target such as when strafing a surface ship. Such a lead angle may, of course, be introduced by proper manipulation of the latch knob 92 and operation of the hand crank I30. Our invention, however, contemplates using the electrical calculating device hereinbefore described as a means for automatically computing the gunnery lead angle to permit the pilot to introduce the gunnery lead angle into the sight without resorting to mental trigonometrical calculations.

If the symbol s' is used to represent the proper lead angle for gunnery, the magnitude of this angle may be expressed by the equation U sin 6 V-i- V (30) 23 I86 (see Fig. 12) which may be arranged as a single-pole double-throw switch movable from a normal position adapting the calculating device for torpedoing calculations to a second position converting the calculating device to the calculation of the gunnery lead angle As is shown in Fig, 12, the switch I88 is interposed between the output of the amplifier stage I12 and the potentiometer I13 so that when the switch is thrown to its second position, this circuit is opened and a circuit is established between the output of the amplifier I12 and a potentiometer I81. The potentiometer I81 is preferably housed within the control member 9 and when the dial f the potentiometer I8! is set to indicate the value of V corresponding to the forward speed of the aircraft.

The voltage 613 is applied to an amplifier stage I 88, the overall gain of which is made equal to K5. Thus the output of the amplifier I88 is The output of the amplifier I88 is connected as indicated at I89 to that input channel of the mixer I82 to which the output of the mixer stage I19 is applied. It will be recalled that there is applied to the other input channel of the mixer I82 a voltage Like the voltages em and en, the voltages an and 611 are so phased that the mixer effects a subtraction of these two. By this the voltage output of the mixer I82 is made proportional to the difference between sin and sin e. As a result, the phase selector I84'and polarized relay I85 are actuated in the manner hereinbefore described in connection with the use of the device as a torpedo director to automatically position the pelorus portion of the sight at the gunnery lead angle t relative to the axis of the aircraft.

Thus in order for the pilot of the aircraft to use the device as a gun sight and to introduce the gunnery lead angle into the setting of the sight, it is only necessary for him to turn the switch I86 to its second position, set the target course arm 91 to alignment with the course of the target, set the potentiometer I10 to correspondence with the velocity of the target, and set the potentiometer I81 to correspondence with the velocity of the aircraft. Thereafter when the sighting line is held on the target, the course of the aircraft will be such as to lead the target by the calculated gunnery lead angle e11=E sin ,6

Calculation of range indication In using the device as a torpedo director, it is necessary in order that the released torpedo may collide with the target ship to release the torpedo from the aircraft at the time the aircraft reaches a release point RP located in accordance with the chosen torpedo travel range. If the torpedo is released either sooner or later than at the point RP. the torpedo will in all probability pass, respectively, behind or in front of the target ship TS instead of colliding with the ship as is desired. It is accordingly necessary that some means be provided for apprising the pilot of the aircraft of his arrival at the chosen release point RP corresponding to his previously selected torpedo travel range R as set up on the potentiometer I'I'I.

Referring again to Fig. 2, the length of the side 2I of the sighting triangle has been represent-ed by the symbo1 Y and the apparent length of the target ship TS as viewed from the release point RF is represented by the symbol L'. It will be noted that the distance Y may be expressed in terms of the apparent length L of the target ship TS and the angle between two sighting lines 302 and 303 directed, respectively, from the release point RP to the bow and stern of the target ship TS. The angle between the lines 302 and 303 may be expressed in terms of the distance S subtended thereby at an arbitrarily chosen distance F from the release point RP. The distance S may be computed from the following equation Employing the symbol L to represent the actual length of the target ship TS, the apparent length L may be very closely approximated by L'=L sin 0 (35) Also it may be stated from the law of sines that R/Y:sin 0/sin a (36) where a is the angle between the sides R and D of the sighting triangle. However The ranging mechanism The device of our invention includes a mechanism associated with the reticule 60 for permitting a direct comparison between the angle defined by S at a distance F from the release point RP and the angle defined by L at a distance Y from RP.

The device for permittin this direct comparison comprises a galvanometer including a permanent magnet 304 secured to a mounting ring 305 which is in turn disposed within the housing portion 45 of the pelorus portion of the sighting device (see Fig. 6). The galvanometer movement is of substantially conventional construction comprising a coil 306 supported upon a pivot shaft 301 for pivotal movement between pole pieces 30B and 309 defined by the permanent magnet 304. The moving coil 305 is normally urged to one position as by means of a restoring spring and is so arranged that the passage of current through the coil will result in a pivotal movement of the coil against the force of the restoring spring.

.In conventional galvanometer constructions the moving coil carries a hand or needle adapted to be moved over a dial to permit a measurement of the current flowing through the coil. According to our invention the hand or needle is supplanted by an opaque member 3I0. This member may be formed of wire or similar small diameter rigid stock. It comprises an outer curved member or horn 3II and an inner curved mem her or horn 3I2, these horns being held in a pre- 25. determined spaced relation to each other by end members 313 and 314, the entire assembly being connected to the moving coil 306 as by radially extending members 315 and 316 and suitably balanced as by means of a conventional counterweight construction.

Reference to Fig. 8 will reveal that the reticule 60 comprises an opaque member defining a horizontal transparent line 311. This line may be formed by actually cutting a thin slot in a piece of sheet metal or like material or, alternatively, the reticule 50 may be made of glass, coated with an opaque substance and the line 311 defined by engraving a line in the opaque substance of sufficient depth to completely penetrate the same. In any event, the reticule 60 is designed to block all of the light emanating from the lamp globe 54 except that which passes through the line or slot 311 and three cross lines or slots 318, 319 and 320.

The cross line 319 is located in the center of the reticule 60 so that the intersection of the lines 311 and 319 define the direction of the sighting line 1. The cross lines 318 and 320 are located equal distances on opposite sides of the vertical center line 319 and are employed for the purpose of assisting the user of the device in estimating distances and the like.

The opaque member 310 previously referred to 'is disposed with its plane parallel to the plane of the reticule 60 and lies closely adjacent thereto. The curved horns 311 and 312 of the member 310 form an inverted bent V and so extend across the horizontal reticule line 311. When the device is used, the reticule appears to define luminous lines corresponding to the lines 31'1320 and the central line of light corresponding to the reticule line 31'! appears to be broken at the points where the members 311 and 312 cross the line 311 and cast their shadow thereon.

The horns 3| 1 and 312 are curved as is clearly shown in Fig. 8 and their relative disposition is such that the point of intersection of each of the horns 31 1 and 312 with the horizontal reticule line 311 occurs on opposite sides of the vertical center line 319 and at equal distances therefrom. Furthermore, the horns 311 and 312 are so positioned that the distance between the points of intersection of these horns with the horizontal reticule line 31 '1 varies in direct proportion to the angular movement of the moving coil 306 to which the horns are secured,

If the focal length of the lens 46 be used as the distance F, the distance between the point of intersection of the horns 311 and 312 with the horizontal reticule line 311 may be made equal to the distance S, and the angle intercepted by the breaks in the horizontal luminous reticule line 311 will then be equal to the angle formed by the apparent length L of the target ship TS when located at the distance Y. Thus, if the moving coil 306 is turned to an angular position such that the distance between the breaks in the luminous reticule line 311 is equal to the distance S, the pilot may, by comparing the apparent length of the target ship as viewed through the sighting device with the apparent distance between the breaks in the luminous line apparently superimposed upon the target ship and the immediately surrounding area, determine whether or not the aircraft has reached the release point RP.

As the aircraft proceeds on its course toward the release point RP generally approaching the target ship and gradually drawing closer thereto,

the apparent length of the target ship will gradually increase and the pilot will be apprised of the fact that he has arrived at the release point RP by the expansion of the apparent size of the target ship until it just exactly extends between the breaks in the horizontal luminous reticule line 311.

In order for this operation to take place. it is only necessary that the moving coil 306 be so moved as to position the member 310 as may be required to make the distance between the intersection of the reticule line 311 with the horns 311 and 312 equal to the distance S as calculated from Equation 38, supra. This result may be obtained by causing a current to flow through the moving coil 306 which is proportional to the calculated magnitude of the distance S.

The electrical calculation of S We have also illustrated by means of the block diagram (Fig. 12) the manner in which a voltage proportional to the distance S may be developed. For this we employ as the source of the voltage the same alternating potential generator 161 as is employed in the calculation of as has been previously described. It will be recalled that the voltage E generated by the source 161 is conveyed to the rotary transformer 104 so that the output voltage thereof is e1=E sin 0 The voltage e1 is applied to the input winding of the immediately adjacent rotary transformer 103 so that the voltage output thereof will be e1a=ei sin 0 (40) e1s=E sin 0 (413 The voltage 1915 is fed to a potentiometer 321 comprising one element of the unit 146 of the control member 9. It will be recalled that the element 145 included a potentiometer 111 which was used to introduce the factor R into the calculation of the lead angle 1 The potentiom-- The voltage cm is fed to an amplifier stage 322, the overall gain of which may be adjusted to be equal to Ks so that the voltage output of the amplifier 322 will be 65 en=E sin 0/R The voltage en is applied to a potentiometer 323 comprising the unit 145 of the control member 9. The dial of this potentiometer is cali- 7 brated in terms of L, the actual length of the target ship TS and this calibration is so arranged that the voltage output of the potentiometer 323 is The voltage are is fed to an amplifier stage 324, the overall gain of which is adjusted to be equal to FKi. Thus the voltage output of the amplifier 324 is ei9=(E'FL sin /R (45) The voltage 619 is fed as indicated at 325 to a normally high gain amplifier 326, the nominal gain of which may be referred to as u.

The output voltage e20 of the amplifier stage 326 is applied by means of a feedback circuit 32'I328 to the input of the amplifier 3 26. The feedback is arranged to be negative; that is, out of phase with the input voltage e19 so as to, in effect, reduce the gain of the amplifier stage 326.

Within the feedback circuit 321-328 we include the rotary transformer I02 which, as will be explained more fully hereinafter, is so arranged in the sighting device and so coordinated with the rotary transformers I 0| and I03 as to have a transformation ratio proportional to the sine of the sum of the angles 5 and 0. The amplifier stage 326 together with the feedback circuit 32'I328 constitutes a negative feedback amplifier. In such an amplifier the overall gain of the system may be expressed by G==u/ (1+uk) G=1/lt (47) Likewise if e1 represents the input voltage to the feedback amplifier and co represents the output voltage of the feedback amplifier, it may be said that e0=iG (48) Comparing Equations 47 and 48, we find that eo=ei/k (49) Applying these general considerations to the feedback stage involving the amplifier 326 and the rotary transformer I02, it will be observed that the function 'sin (0+0) is the feedback con- I stant and corresponds to k of Equation 49 while the input voltage e19 corresponds to c1 and the output voltage e20 corresponds to 60. It may thus be seen that e2o=e19/Sin (6+0) (50) EFL sin 0 It will be noted that when ,8 equals as is the case when the motor I32 has operated to move the sighting device through the angle 18 corresponding to the calculated lead angle o, Equation 51 becomes identical with EFL sin 0 Comparing Equation 52 with Equation 38, supra, will show that Thus the output voltage can is directly proportional to the calculated value of S. This prothat unless provision is made for preventing the occurrence, an excessive voltage will be applied to the coil 306 whenever the target course arm 91 and the pelorus portion are so positioned with respect to each other as to provide a value of (3+0) less than :45" or greater than i-l35.

This occurrence is prevented by employing a gain limiting circuit which includes a rectifier 392, the input of which is coupled as at 393 to the output of the amplifier stage 326, and the output of which is connected as at 394 to control the gain of the amplifier stage 326 in such manner as to produce a reduction in gain as a result of an increase in the output potential of the rectifier 392.

The rectifier 392 is preferably so biased as to prevent any rectifying action from taking place until the alternating potential applied to the input thereof rises to a value equal to the voltage corresponding to maximum deflection of the galvanometer.

When the output voltage of the amplifier stage 326 rises to a value exceeding that corresponding to maximum deflection of the galvanometer, the rectifier 392 will begin to rectify and the resulting direct potential is so applied to the amplifier stage 326 as to reduce the gain thereof and produce a corresponding reduction in voltage generated thereby. The rectifier 392 thus operates to prevent any appreciable rise in the voltage applied to the galvanometer coil 305 above that corresponding to a value of (0+0) equalling :45 or i and thus serves to prevent injury to the moving coil 306 of the galvanometer.

Reference has been had hereinbefore to the fact that the rotary transformer I02 is so coordinated with respect to the rotary transformers IM and I03 as to cause the transformation ratio to be proportional to the sine of the sum of the angles p and 0. The manner in which this result is achieved is illustrated diagrammatically in Fig. 11. In this diagram the numeral M is used to represent the axis of rotation of the rotary transformers IOII04. The arrows bearing the reference characters IOIR, I02R, I03R and I04R are used to, respectively, designate the rotors of the rotary transformers I 0 II 04.

In a similar manner the reference characters IOIS, I028, I038 and IMS are used to designate the stators of the respective rotary transformers I0 II04. It will be recalled that the stators I036 and W453 are fixed as by means of the screws I05a to the pelorus portion of the sight, this securing of the stators I03S and N48 being indicated at 330 and 33I, respectively, in Fig. 11.

It will likewise be recalled that the rotor IOIR of the transformer IOI is likewise fixed to the pelorus portion of the sighting device by means of the split plug II4. This fixing of the rotor I MB is indicated at 332 in Fig. 11. The stators IOIS and |02S of the rotary transformers MI and I 02 are secured to each other and to the lower notch plate I08 so that when the notch plate I08 is latched to the fixed portion 34, the

29 angle between the rotor IOIR and stator IIHS will be equal to ,3, this fixing of the stators IOIS and I02S being indicated by the dashed line 333 in Fig. 11.

Similarly, the rotors IIIZR, I03R and IMR, are each secured to each other and to the target course arm 91 as by connecting the shaft 99 to each of these rotors. This interconnection of the rotors I02R,I04R is indicated in Fig. 11 by the dashed line 334.

In Fig. 11 we have illustrated the target course arm 9'! as having been revolved through an angle relative to the sighting line I. Since the stators H138 and IMS are fixed to the pelorus portion, this results in disposing the rotors IDZR, I03R and IMF. at an angle a relative to the stators. This angular relationship is diagrammatically illustrated in Fig. 11.

Similarly, in Fig. 11 we have illustrated the pelorus portion and the sighting line I defined thereby as having been swung through an angle 6. Since the rotor IOIR is movable with the pelorus portion and the stators IOIS and MRS are fixed to the notch plate I08, this swinging of the pelorus results in angularly shifting the stators IOIS and H328 through the angle ,3 relative to the rotor IOIR.

Referring particularly to that portion of Fig. 11 illustrating the rotor and stator of the transformer I02, it will be noted that the stator I02S has been shifted in one direction by the angle 18, whereas the rotor has been shifted in the opposite direction through the angle 0. As a result the angular relation between the rotor IMF. and the stator I02S comprises the sum of the angles 5 and 0. Thus the transformation ratio of the transformer I02 is made directly proportional to the sine of the sum of the angles 5 and 0.

The operation of the sighting device with the hereinbefore described ranging feature is not materially different from that which has already been described in connection with the operation of the calculator which determines the angle and shifts the sighting device to the corresponding position. At the time the pilot of the aircraft is operating the control member 9 by setting up on the various dials thereof the values of the factors H, V, U and R, he will at the same time set on the corresponding dial the value of L corresponding to the actual length of the target ship TS. This factor, like the factor U, is known to the pilot of the aircraft as soon as he identifies the nationality and type of the target ship TS. When this operation is completed, the mechanism operates in the manner hereinbefore described to direct the sighting line in such manner that the launched torpedo will follow a course making the lead angle with the sighting line,

At the same time the calculator just described actuates the galvanometer so that the reticule pattern observed by looking through the si hting device is characterized by having two breaks in the horizontal luminous line. The pilot of the aircraft continues along the torpedo course by so guiding the aircraft as to keep the intersecting center lines of the reticule pattern on the target ship. When the aircraft is at a point disposed farther from the target ship TS than the proper release point RP. the apparent length of the target ship as viewed in the sighting device will be less-than the distance between the breaks in the horizontal reticule line. As the distance between the aircraft and the target ship is gradually reduced, the apparent size of the target ship will correspondingly increase. When the apparent length of the target ship has increased to a point where it appears to exactly fill the gap between the two breaks in the horizontal reticule line, the pilot of the aircraft is thereby apprised of the fact that he has reached the proper release point RP and thereupon promptl launches the torpedo.

Operation At this point it is desired to point out a different possible mode of operation of the device of our invention which may be used to advantage when the factors U and L are known before the target ship is sighted as by reason of previous flights over the target area or by reason of information relayed to the pilot of the aircraft by radio. Under such circumstances the pilot may decide or be instructed as to the range at which the torpedoing operation will be performed, the height from which the torpedo will be released and the forward speed of the aircraft at the time the torpedo is launched. Under these circumstances the pilot may set up each of the factors H, V, U, L and R on the control member 9 before the target ship is sighted.

The pilot may then proceed until the target ship is sighted. With the pelorus positioned to take a sight on the target ship TS, the target course arm 91 is set to parallelism with the course of the target ship TS and the control knob 92 is then manipulated to drivably engage the pelorus portion of the sighting device with the electric motor I32. This completes the operations which the pilot must perform in order to place the sight in readiness for use. Thereafter it is only necessary for him to so change the course of his aircraft as to bring the sighting line I to again bear upon the target ship and then follow that course until the target ship appears to fill the gap between the breaks in the horizontal reticule line. When this condition obtains, the torpedo is released and will, barring a subsequent change in course by the target ship, collide with the target ship at the collision point 0.

The sighting device of our invention is particularly adapted to permit the pilot of the aircraft to change his mind about any of the underlying factors involved at any time during the approach to the target. He may, for example, decide upon arriving at closer range that the vessel is of different length or moving at a different speed than assumed previously or he ma venture a better estimate of the targets course or he may decide to fly slower or faster, higher-or lower or to launch the torpedo from a closer range than had been his earlier strategy. All he has to do is to correctly readjust the dial members I52 of the control units I42--I46 or the position of the target course arm 91. The electrical calculating mechanisms hereinbefore described will immediately effect the proper correction of the. azimuth 'angle 5 of the notch plate I08 and the proper correction of the position of the galvanometer horns 3| I and 3I2 to conform to the newly determined conditions.

From the foregoing it will be observed that we have provided a sighting device which includes the necessary mechanism for taking into account each of the various factors which go to determine the location of the proper torpedo or pro- J'ectile course which will be required in order to produce the desired collision between the projectile and the target.

Furthermore, the device of our invention operates to automatically perform the necessary trig- 

